Solar tracking apparatus

ABSTRACT

A solar tracking apparatus which is movable from a morning position to an evening position, the apparatus comprising a support means to which a solar device can be supported, a cylinder, the cylinder including a ram which is extendable from and retractable into the cylinder, an expansion chamber which forms part of or which is in fluid connection with the cylinder, a liquid in the cylinder and the expansion chamber, the liquid having a boiling point which is greater than the maximum operating temperature of the cylinder and the expansion chamber, a return means to cause the apparatus to be returned to the morning position, and rotation means associated with the ram to rotate the apparatus from the morning position to the evening position upon extension of the ram.

FIELD OF THE INVENTION

This invention is directed to a solar tracking apparatus which can beused in association with solar collector panels or any other devicewhich requires tracking. The invention is particularly directed to anapparatus that does not require any electric motors, sensors, or othercomplicated devices to enable the apparatus to track the movement of thesun.

BACKGROUND ART

There are many devices that use the energy of the sun to provide auseful benefit. As an example, solar cells are often used to convert theenergy of the sun into electricity. These devices are often used inremote locations to power pumps, lights, telecommunication devices andthe like and must be extremely robust and reliable. There are also otherdevices that require the energy of the sun, for successful operation,such as water heating devices. The effectiveness of these devices isgenerally improved if the device can track the movement of the sun toenable the device to absorb as much as possible of the sun's energy.Therefore, it is well known to provide some form of solar trackingapparatus.

A common type of apparatus uses one or more photoelectric cells whichare operatively associated with some form of electric drive motor. Thereare several disadvantages with this type of apparatus including thefragile nature of the photoelectric cells, and the need to have a sourceof electric power, such as battery power, or electricity generated fromthe solar cells. This type of apparatus requires a relatively highdegree of servicing, maintenance, and repair, and therefore does notfind particular use in remote locations.

An attempt has been made to do away with the need for electric motorsand photoelectric cells. For instance, international patent applicationWO 92/11496 describes an apparatus which has two cylinders. Eachcylinder is filled with a low boiling liquid (which can include ether).Around each cylinder is a parabolic reflector. One cylinder and itsparabolic reflector faces the east and the other cylinder and itsparabolic reflector faces the west. As the sun rises in the east, thesun's rays will be concentrated by the parabolic reflector onto the eastfacing cylinder to boil the liquid in the cylinder to create a gas whichcauses the cylinder ram to extend and this causes rotation of aframework on which solar cells are attached. An advantage with thisapparatus is that photoelectric cells and electric motors are notrequired. However one main disadvantage is that the parabolic reflectorsare relatively high maintenance and the reflector (or the transparentglass or plastic cover) must be kept very clean. Also, significant heatis required to boil the liquid into the gas which means that theapparatus may not work immediately. Moreover, working with gas requiresparticular design principles and the overall effect is that this type ofapparatus is not entirely reliable and robust.

A further disadvantage with many existing solar tracking devices is thatthe device does not return back to the “east facing” position during thenight and only does so at the beginning of the next day. This makes thistype of device less efficient.

A further disadvantage with many existing solar tracking devices is thatthe devices are not particularly stable or effective under high windconditions

Therefore, there would be an advantage if it were possible to develop asolar tracking apparatus that did not require photoelectric cells thatdid not require an electric motor to track the apparatus, that did notrequire parabolic reflectors, and that did not require boiling a liquidinto a gas to provide the working force for a cylinder.

It will be clearly understood that, if a prior art publication isreferred to herein, this reference does not constitute an admission thatthe publication forms part of the common general knowledge in the art inAustralia or in any other country.

OBJECT OF THE INVENTION

It is an object of the invention to provide a solar tracking apparatuswhich may overcome at least some of the above-mentioned disadvantages orprovide a useful or commercial choice.

In one form, the invention is directed to a solar tracking apparatuswhich is movable from a morning position to an evening position, theapparatus comprising a support means to which a solar device can besupported, a cylinder, the cylinder having a ram which is extendablefrom and retractable into the cylinder, an expansion chamber which formspart of or which is in fluid connection with the cylinder, a liquid inthe cylinder and the expansion chamber, the liquid having a boilingpoint which is greater than the maximum operating temperature of thecylinder and the expansion chamber, a return means to cause theapparatus to be returned to the morning position, and a rotation meansassociated with the ram to rotate the apparatus from the morningposition to the evening position upon extension of the ram.

Typically, the morning position will be the east facing position orposition which faces substantially east (it being appreciated that thesun does not rise exactly in the east over a year) and the eveningposition will be the west facing position or position which facessubstantially west.

The solar device may comprise solar cells or other devices which absorbsolar radiation, these including water heating devices, and the like,and no particular limitation should be placed on the term “solardevice”. The term “solar device” can comprise a single device, aplurality of devices and the like.

The expansion chamber can be positioned such that liquid in theexpansion chamber is initially heated mainly by the ambient airtemperature to cause initial extension of the ram , and is then heatedmainly by solar radiation [i.e. direct contact with the sun] to causefurther extension of the ram.

Thus, the apparatus uses the thermal expansion of a liquid to rotate theapparatus from the east to the west and does not require the use of anyelectric motors, photovoltaic cells, or the need to boil a liquid (whichrequires parabolic reflectors or other strong heating means). In anembodiment, the apparatus moves by combination of radiant heat (directcontact with sunlight) and ambient heat (air temperature). The expansionchamber is gradually heated by the surrounding air as the sun rises inthe morning causing the liquid to expand. The expansion causes the ramto displace which in turn causes rotation of the apparatus. Theapparatus is rotated steadily until it approaches in approximatelyhorizontal position which will typically be during midday. As the sunpasses the midday position, the expansion chamber is progressivelyexposed to direct sunlight (radiant heat) which causes further expansionof the liquid and therefore further rotation of the apparatus. Duringnight-time the liquid cools and contracts permitting the return means torotate the apparatus back to the easterly position.

The apparatus preferably uses a clever combination of ambient heatingand direct solar heating to enable the apparatus to track from the eastto the west even as the ambient temperature decreases in the afternoon.Thus, the apparatus can initially use primarily ambient heating toexpand the liquid to cause the apparatus to begin tracking from the east(morning) position to the west (evening) position, and can then usedirect solar heating to cause the liquid to expand even further (andtherefore extend the ram even further) even when the ambient temperaturebegins to decrease in the afternoon.

In one form, this is achieved simply yet effectively by positioning theexpansion chamber on the apparatus in such a manner that it caninitially absorb heat from the surrounding air and later on, when theapparatus is partially rotated, the expansion chamber is exposeddirectly to the sun's radiation.

In a broader form, the invention resides in a solar tracking apparatuswhich uses volumetric expansion of a liquid only as the motive source.

The solar tracking apparatus can be used to support any device thatrequires solar energy. The device will typically comprise solar cellsbut the invention need not be limited to this precise use and theapparatus can also be used to support and rotate other devices which mayinclude water heating devices, air heating devices, or any othersuitable device.

The support means can be quite varied providing that it functions tosupport a solar device or other device that requires solar energy. Ifthe solar device comprises solar cells, the support means will typicallycomprise a support platform, support frame, support bracket, supportingrods, supporting rails, a supporting grid and the like. Other types ofsupport means may be used depending on the solar device which is to besupported.

The apparatus comprises at least one cylinder which has a ram. Thecylinder will preferably be such that the stroke of the ram is between50-400 millimeters and more preferably between 50-200 millimeters. Theinternal volume of the cylinder can vary and will typically be between50-500 milliliters. For larger systems, the cylinder may be larger or aplurality of cylinders may be provided.

The expansion chamber may comprise a hollow member which will typicallycomprise a tube. The tube will typically be liquid tight and be in fluidcommunication with the cylinder. The expansion chamber will typically befilled with a liquid which is selected to provide a desirable increasein volume upon increasing temperature of the liquid. The expansionchamber will typically have a length of between 10-200 centimeters and adiameter of between 10-100 millimeters. This of course can varydepending upon the size of the apparatus. The expansion chamber may becoupled directly to the cylinder or may be coupled indirectly to thecylinder by means of a connecting tube or other form of conduit. If aconnecting tube is provided, it may be flexible. The expansion chambermay comprise a number of sub-chambers which are either connected to eachother or connected to the cylinder. The expansion chamber may be coatedor otherwise treated to improve absorption of radiant heat and/orambient heat. For instance, the expansion chamber may be coated with ablack radiation absorbing paint. If desired, insulation means may beprovided to minimize undesirable cooling of the liquid within theexpansion chamber. Thus, it is envisaged that the expansion chamber maybe coated with a radiation absorbing paint on the surface of the chamberwhich will be in direct contact with the sun's rays, and may beinsulated on parts of the chamber which will not be in direct contactwith the sun's rays. The expansion chamber may also form part of thecylinder and may comprise a simple extension of the cylinder.

The liquid which is used in the chamber and the cylinder may be selectedfrom any liquid which has a suitable volumetric expansion coefficient.However, it may also be desirable to choose a liquid which does notcause corrosion of the internal parts of the apparatus, can assist inlubricating the apparatus and the like. Various liquids can be usedalthough it is desirable to ensure that the boiling point of the liquidis higher than the working temperature of the apparatus. Even in a harshdesert environment, it is envisaged that the working temperature of theapparatus will not exceed 60 degrees centigrade (it being appreciatedthat the apparatus does not require any parabolic reflectors and thelike to greatly increase the temperature of the liquid) and therefore itis envisaged that a suitable liquid will be one having a boiling pointof >60 degrees centigrade. It is found that a mineral oil such as anengine oil is suitable, and the oil as well as having a suitable boilingpoint, can also lubricate and prevent corrosion of the internalcomponents of the apparatus. Other oils and hydrocarbons may also besuitable. Certain plant oils are also suitable and these can includecanola oil, sunflower oil, peanut oil, grape seed oil and the like.Certain liquid alcohols are suitable liquids and especially alcoholshaving a boiling point of >60 degrees centigrade. Ethanol is found to bea suitable alcohol as is propanol, isopropanol, and butanol. Highboiling point ethers, ketones, esters and the like may also be suitableliquids, it being appreciated that the liquid can be chosen based on itsvolumetric expansion coefficient, cost, safety (i.e. toxicity andflammability), corrosive effects on the cylinder etc.

It is preferred that the entire expansion chamber and cylinder arefilled with the liquid as any gas may reduce the effectiveness of theextension and retraction of the ram.

The apparatus may be provided with a return means to cause the apparatusto return back to the morning position during nighttime. The returnmeans may comprise a simple spring or a plurality of springs) whichis/are sufficient to return the apparatus back to the morning positionbut does not unduly interfere with the operation of the ram. However,the return means may comprise other types of biasing means such aselastic members, compressive members and the like. It is also envisagedthat the return means may comprise a “vacuum cylinder” which becomesprogressively more under vacuum during rotation of the apparatus fromthe morning position to be evening position and then can return back tothe rest position causing the apparatus to move back from the eveningposition to the morning position. It is also envisaged that theapparatus may be weighted such that gravity will cause the apparatus toreturn to the morning position.

The apparatus has a rotation means which is associated with the ram torotate the apparatus from the morning position to the evening position.The rotation means may comprise a simple mechanical coupling which isreliable and robust. The mechanical coupling may comprise a crank armwhich is attached to a pivot tube, the pivot tube being attached to thesupport means to rotate the support means from the morning position tothe evening position and vice versa. Alternatively, the mechanicalcoupling may comprise a rack and pinion arrangement where the rack isattached or forms part of the ram. Various other types of rotation meansare envisaged which can be used to convert the linear motion of the raminto rotating motion of the apparatus.

The apparatus may also be provided with an additional rotation means toenable the apparatus to rotate about substantially vertical axis. Inthis version, the apparatus may be pre-inclined and rotated about avertical axis. This additional rotation means may also comprise acylinder and ram which may be substantially as described above exceptthat the ram causes pivoting or rotation of the apparatus about avertical axis.

The apparatus may be mounted a support post, or any other type ofsupporting member.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described with reference to thefollowing drawings in which:

FIG. 1 is an isometric view showing one embodiment of a two-axis trackerfor a single photovoltaic panel.

FIG. 2 and FIG. 3 are sectional views of the device depicted in FIG. 1showing two positions of rotation

FIG. 4 is a sectional view of the hydraulic ram shown in FIG. 1

FIG. 5 is an exploded view of the device shown in FIG. 1

FIG. 6 is an isometric view of a preferred embodiment of a tracker andsupport frame for a multiple array of photovoltaic panels.

FIG. 7 is an exploded view of the device shown in FIG. 6

FIGS. 8A and 8B are partial sectional views of the device shown in FIG.6 showing two positions of rotation.

FIGS. 9A and 9B are side views of the device depicted in FIG. 6 (frameremoved) showing north south orientation method.

FIG. 10 shows a sectional view of an alternative thermal hydrauliccylinder, using electric power to heat the liquid.

FIGS. 11A and 11B Illustrate the view of FIG. 9 with the addition of athermal hydraulic cylinder illustrated in FIG. 4 to control north-southorientation.

FIGS. 12A and 12B illustrate a vertical rotation modification.

BEST MODE

FIGS. 1-5 shows a single panel solar tracker in a preferred embodiment.

In FIG. 1 to FIG. 5, there is shown an embodiment where support post 9has slots cut into the upper end to accommodate rotational displacementof the axis pivot tube 12. Post 9 has location holes bored through tohouse the north-south axis pivot bolt 7 and north south axis-positioningclamp 8. Movement of pivot tube 12 is restricted by axis bolt 7 so thatit pivots in the north south direction only. Right-angled axis pin 30and spring retainer tube 31 (see FIG. 5) are fixed to axis tube 12. Axistube 12 is pierced to rotatingly mount the top end of clamp pin 14. Bothends of tube 12 are threaded for shoulder bolts 11. Lateral supportbrackets 5 and 6 are pivotally attached to tube 12 by bolts 11 and areheld parallel by rod 10. Clamp plates 18 fix solar panel 1 to brackets 5and 6. Locating holes provided in the inner end of brackets 5 and 6pivotally retain expansion tube and hydraulic cylinder assembly 2 and 3.The hydraulic cylinder 3 is comprised of an outer pressure tightcylinder, a linear actuator ram 4, an adjustable gland or piston 15, adamper plate 16 and sealing “O” rings 17. A ferrule fixed to theoutermost end of ram 4 is rotatingly mounted on right-angled pin 30.

The operation of the afore described embodiment commences when the sunbegins to rise above the eastern horizon and the ambient air temperatureincreases; the liquid contained within expansion tube 2 and cylinder 3also begins to expand. The liquid contained therein expands at a muchgreater rate than the surrounding container and a pressure is createdwhich impinges on the cross sectional area of the ram 4 thus displacingit outward proportionally to the volumetric expansion of the liquid.

The liquid used in the device has a volumetric expansion rate ofapproximately 0.085 cubic centimeters per degree Celsius increase;therefore 1 liter of liquid will expand to 1008.5 cc when raised intemperature by 10 degrees Celsius. Liquid is considered to be virtuallyincompressible therefore the potential pressure created by thisexpansion is extremely high and can be considered limited only by thestrength of the container which holds it. In the afore describedembodiment this pressure is used to force ram 4 outward with a limitingfactor of the enclosing structure and “O” rings 17.

The embodiment afore described is designed to rotate a P.V.(photovoltaic) panel 1 of approximately one square meter and contains avolume of liquid sufficient to displace an actuator ram of 12 mm dia.(1.13 square cm. cross sectional area) with a rise in temperature of 10degrees Celsius, by 75 mm. and a pressure which is determined by thephysical housing structure and sealing rings.

The sealing rings are conventional “O” rings, which are nominallyconsidered to have a safe operating pressure of 1.03 MPa. This pressurecan provide a rotational force of 119 kg, which is more than needed torotate the panel. The excess force provided can be used to dynamicallycontrol the positioning of the panel under high wind loads bytransposing the externally applied forces to the internal structure oftube 2 and cylinder 3 and elastically deforming said structure thusmaintaining an equilibrium of forces during the day. This system hasbeen tested and proven to maintain the face of a P.V. panel to within 10degrees of perfect orientation, which is 98.5% of best possiblepositioning.

Different locations require different volumes of liquid and/or a liquidthat has a higher or lower expansion rate than the embodiment aforedescribed; this is easily compensated for by adjustment of the threadedgland 15 and/or using an expansion liquid that has characteristicsbetter suited to the climatic conditions of the installation site.

Ambient temperatures usually increase at a steady rate during a normalclimatic day and reach a maximum at about an hour after midday. When theincrease in air temperature has rotated the P.V. panel to the horizontalposition the expansion tube 2 is progressively exposed to solarradiation where the liquid contained therein continues to expand pushingthe panel gradually toward the west. The liquid contained in tube 2 andcylinder 3 cools overnight permitting spring 13 to return solar panel 1to the eastern most position. The liquid is selected for its optimumthermal expansion properties and the volume contained within thecylinder and the expansion tube is calculated to provide sufficientexcess volume when heated to displace the ram outward from the cylinderand to rotate the panel assembly through approximately 70° by convectionheating only.

FIG. 4 shows a cross sectional view of hydraulic cylinder 3. Damperplate 16 is shown as a 3-piece assembly being composed of two outerplates of rigid material sandwiching a layer of resilient material thatseparates chambers 21 and 22 compelling excess fluid to flow to and frovia channel 20 bored into ram 4. This arrangement produces a dampeningeffect when the solar panel is exposed to high wind velocities. Liquidis permitted to slowly pass through a small canal maintaining a pressurebalance in the chambers on either side of the damper plate. Thehydraulic pressure provided by the expanding liquid is very high andcombined with the damper plate the system readily handles high windspeed.

FIG. 6-FIG. 9 show another embodiment according to the invention where aplurality of solar panels 1 can be rotated simultaneously using the samebasic expansion tube and hydraulic cylinder assembly as previouslydescribed. In this embodiment expansion tube 2 is located in a gapbetween two rows of solar panels 1, shown as phantom lines in FIG. 6 andpartly shaded by frame 40. A ferrule fixed to the outermost end of ram 4is rotatably mounted to north south axis bracket 24 by clevis 8 and pin32. Circular plate 23 fixed to post 9 has a cam shaped slot and acentral hole pierced through it (see FIG. 7). Bracket 24 is rotatablypinned to plate 23 by axis bolt 7 and clevis 8 passes through the slotin bracket 24 and cam slot in plate 23.

FIG. 9 shows that when bracket 24 and attached assembly is manuallyrotated to compensate for seasonal conditions, clevis 8 is moved by thecurved surface of the cam shaped slot in plate 23 impinging on it.Clevis 8 moves closer to the cylinder 3 and attached ram 4 is movedfurther into said cylinder 3. This procedure automatically compensatesfor the reduced volume of liquid that is caused by seasonal cooling.

FIG. 8 shows that the principal of operation of the embodiment shown inFIGS. 6-9 is similar to that shown in the embodiment described by FIGS.1-5.

FIG. 11 shows a method of positioning the PV panel to increase thepotential output of the said panel through the application of ahydraulic cylinder as described by FIG. 4. The cylinder 36 contains aliquid that is calculated to provide an additional expansion volume sothat no displacement of the ram will occur during the mid winter maximumtemperature but will provide maximum expanded volume during the summermaximum daytime temperature. Cylinder 36 is connected via lower support33 and upper support 34 to post 9 and is pivotally connected at 35 tosupport 34.

FIG. 10 shows an alternative method of heating and expanding the liquidcontained in hydraulic cylinder 3 where an electric current is providedby battery 26 through a circuit containing a rheostat 28, a cam operatedmicro switch 27 and heating element 25. The power required to rotate thePV panels is very low and for the operation of a one square meter panel,is less than one watt when cylinder 3 is encased with adequate thermalinsulation material 37.

FIGS. 12 a and 12 b illustrates an embodiment to enable the apparatus torotate about a vertical axis defined by post 9. This is achieved using a“rack and pinion” mechanism. Specifically, cylinder 3 contains amodified ram 4. Ram 4 is modified by having a rack 40 at the end of theram 4 (particularly illustrated in figures 12 b). The upper part of post9 is provided with a pinion gear 41. Extension and retraction of ram 4will cause rotation of the entire apparatus about post 9. A flexiblehose 46 connects the expansion tube 2 to cylinder 3, cylinder 3 and ram2 being provided with attachments nipples 38. Thrust washers 42, 43 areprovided on the either side of pinion 41. Ram 4 can cause rotation of upto 270°. The apparatus illustrated in figures 12 a and b is for theSouthern Hemisphere and would have components fabricated in mirrorreverse for the Northern Hemisphere.

It is envisaged that a windshield may be used to prevent excessive airconvection currents from reducing the temperature of the liquid in theexpansion tube or cylinder. The windshield may comprise a clear memberwhich will still allow the expansion tube to absorb radiant heat.Alternatively, the windshield may be positioned in such a way to nothinder radiant or ambient heating but to still provide a shield againstcooling winds.

It is further envisaged that the apparatus may be attached to a numberof other supports which can also supports solar cells and where theother supports are all controlled by the cylinder on the apparatus usingconnecting means which may comprise rods, cables and the like. In thismanner, the cylinder on the apparatus can be used to rotate a number ofseparate devices and the other devices can be quite simple constructionswithout a cylinder.

Although an advantage of the invention is that it does not requiremotors, batteries and the like, it is envisaged that the apparatus mayinclude a small electric heater to heat the liquid if desired (see FIG.10). The electricity for the small electric heater can be supplied bysome of the solar cells.

The apparatus has many advantages. One advantage is that the liquidremains in a liquid state throughout the full operational parameters ofthe apparatus and the liquid is not artificially heated (for instance byparabolic mirrors) and is heated only by solar radiation or ambient airtemperature.

Throughout the specification and the claims (if present), unless thecontext requires otherwise, the term “comprise”, or variations such as“comprises” or “comprising”, will be understood to apply the inclusionof the stated integer or group of integers but not the exclusion of anyother integer or group of integers.

It should be appreciated that various other changes and modificationscan be made to any embodiment described without departing from thespirit and scope of the invention.

1. A solar tracking apparatus movable from a morning position to anevening position, the apparatus comprising a support means to which asolar device can be supported, a cylinder, a ram which is extendablefrom and retractable into the cylinder, an expansion chamber which formspart of or which is in fluid connection with the cylinder and which ispositioned at a point below the solar device, a liquid in the cylinderand the expansion chamber, the liquid having a boiling point which isgreater than the maximum operating temperature of the cylinder and theexpansion chamber such that the liquid does not undergo a phasetransformation, a return means to cause the apparatus to be returned tothe morning position, and rotation means associated with the ram,whereby extension of the ram causes the apparatus, including theexpansion chamber, to rotate over an angle of up to 270° from themorning position to the evening position.
 2. The apparatus of claim 1,wherein said support means includes a vertical post, and a rack andpinion mechanism is defined between said vertical post and said ram, torotate the apparatus about a vertical axis to position, said apparatusfor the Northern or Southern Hemisphere.
 3. The rack and pinionmechanism of claim 2 comprising a pinion gear located at the upper endof said vertical post, and a rack defined at the end of said ram, saidrack and pinion mechanism rotating said apparatus.
 4. The apparatus ofclaim 1, which has a west-facing edge, the expansion chamber beinglocated under the west-facing edge.
 5. The apparatus of claim 1,comprising a plurality of solar devices supported by the support means.6. The apparatus of claim 1, comprising a post, the support means beingattached to the post and being able to swivel relative to the post. 7.The apparatus of claim 1, wherein expansion of the liquid in theexpansion chamber causes the support means to swivel relative to thepost.